PURPOSE: As the most recent epidemiological studies provide no definite conclusions about the effects of 50/60 Hz magnetic fields (MFs) on the incidence of leukaemia in humans, animal models in a well-controlled environment are useful for evaluating the possibility of an association between MFs and leukaemia. The present study was designed to determine whether 50 Hz magnetic fields can alter the progression of leukaemia. MATERIALS AND METHODS: A well-characterized model of transplantable acute myeloid leukaemia in rats was used for the first time. This model is closely related to human acute myeloid leukaemia, the type most frequently reported in epidemiological studies of adults. After leukaemic cell implantation, rats were exposed to a sinusoidal 50 Hz MF of 100 microT for 18 h a day, 7 days a week, throughout leukaemia progression. The parameters investigated were: survival time, body weight, haematologic parameters, infiltration of blood, bone marrow, spleen and liver by leukaemic cells. RESULTS: The results showed no significant changes (p > 0.05) in leukaemic MF-exposed versus unexposed rats for any of the parameters involved in leukaemia progression. CONCLUSION: These data do not support the hypothesis that 50 Hz magnetic fields influence leukaemia progression in humans.